1. Field of the Invention
The present invention relates to the art of flash butt welding and is specifically concerned with a method of flash butt welding, wherein a reciprocating or an oscillatory motion of at least one of the parts being joined together is superimposed on the main translational motion of the parts.
2. Description of the Prior Art
A method of flash butt welding, wherein an additional oscillatory motion along the direction of approach is imparted to one or to both of the parts being joined together finds at present an ever extending commercial application. The method offers the advantages of both the straight flash butt welding (a uniform heating of the metal over the section of the parts welded together, a stable quality) and the resistance butt welding (low fusion loss of the metal, the possibility of utilizing the whole of the installed capacity of welding transformers). The advantages inherent in such a method of welding allow producing welded joints featuring high mechanical properties (with a strength equal to that of the base metal) and to reduce the welding time by a factor of two to three.
This method of welding (British Pat. No. 1,162,073) consists in fusing by an alternating current the ends of the parts being welded together and concurrently causing the parts to continuously approach each other, with imparting to at least one of the parts an oscillatory motion whereby additional relative movements of the parts being welded towards each other and away from each other are accomplished.
The additional oscillatory motion causes the spark gap to vary. A linear variation in the size of the spark gap results in a variation of the resistance in the welding circuit.
As the parts being welded are moved away from each other, the area of contacts therebetween decreases and the resistance increases and while they are being relatively moved towards each other the said area of contacts increases and the resistance decreases.
At the end of the parts being relatively moved away from each other and at the beginning of their being relatively moved towards each other, there occur, generally, explosions of contacts (fusion). The amount of expelled metal, the thermal efficiency, and the rate of fusion depend upon the instantaneous value of the welding voltage at the moment of the explosion of a contact. It should also be pointed out that the probability of explosion of relatively large-size contacts during a relative movement of the parts towards each other is low.
The method disclosed in the British Pat. No. 1,162,073 takes no consideration of the above factors. In accomplishing this prior art method, widely varying instantaneous values of the welding voltage may correspond to a definite resistance across contacts, which lengthens the welding time and reduces the thermal efficiency.
The invention has as its aim to provide a method of flash butt welding, which cuts down the fusion loss of metal, increases the rate of heating, and allows the productive capacity of the butt-welding machines to be raised.